1. Field of the Invention
The present invention relates to a semiconductor device having a through (penetrating) electrode for electrically connecting a semiconductor substrate to another semiconductor substrate, semiconductor device or equipment, and to a method of manufacturing the same.
2. Description of the Background Art
A semiconductor device having a through electrode extending from a front surface to a back surface of a semiconductor substrate has been conventionally used. A conventional semiconductor device is formed with a method as described below.
In the method, a first hole for embedding a through electrode having a prescribed depth and an interconnection to be connected to the through electrode are first formed on a semiconductor substrate. Then, an insulation film is deposited to cover an inner peripheral surface of the first hole and the interconnection. Thereafter, a portion of the insulation film inside the first hole is removed, in which portion the through electrode will be formed. Therefore, the insulation film remains along the inner peripheral surface of the first hole. As a result, a second hole is formed inside the first hole with a surface of the insulation film. In this situation, the insulation film outside the first hole is removed so as to expose a portion of the interconnection.
Then, a conductive film (a seed layer) is deposited along an upper surface of the insulation film and a surface of the second hole. Electroplating is performed using the conductive film as a cathode to embed a metal in the second hole. The metal is embedded in a columnar form. Thereafter, a back surface of the semiconductor substrate is polished with mechanical or chemical polishing or a combination thereof until a bottom surface of the columnar metal is exposed. As a result, the bottom surface of the columnar metal is exposed on the back surface of the semiconductor substrate. This columnar metal serves as a through electrode.
In the method of manufacturing the semiconductor device having the through electrode as described above, particularly to form the through electrode having a large aspect ratio, it is necessary to form the insulation film and the seed layer having good covering properties along the inner peripheral surface and a bottom surface of the first hole having a large depth and a small opening. It is, however, extremely difficult to process as described above.
When the covering property of the insulation film described above is not good, electrical leakage in the semiconductor substrate and a malfunction of a semiconductor circuit will result in reduced yield and reliability of the semiconductor device. In addition, when the covering property of the seed layer described above is not good, the yield of the semiconductor device will be reduced because, during the electroplating, a void is generated in the metal to be the through electrode.
In the step of embedding the metal in the second hole with electroplating, the metal is basically formed well in a portion in which an agent solution flows at a high rate. Therefore, the metal is formed sufficiently in an upper portion of the second hole, in which portion the agent solution flows at a high rate, while the metal is formed insufficiently in a portion near a bottom surface of the second hole, in which portion the agent solution flows at a low rate. That is, as the metal grows faster in the upper portion than in a lower portion in the second hole, the upper portion of the second hole will be closed while the lower portion of the second hole has a void therein.
The above-described problem is resolved by decreasing aspect ratios of the first and second holes. To decrease the aspect ratios, openings of the first and second holes may be enlarged or depths of the first and second holes may be decreased.
Enlargement of openings of the first and second holes, however, inhibits a size reduction of the semiconductor device. To decrease depths of the first and second holes, on the other hand, a thickness of the semiconductor substrate must be decreased. This leads to decreased rigidity of the semiconductor substrate. As a result, reliability of the semiconductor device is decreased. In addition, manufacturing steps will be increased if a support board is fixed to the semiconductor device to reinforce the semiconductor substrate when a thin semiconductor substrate is formed. Furthermore, the support board and an adhesive for adhering the support board to the semiconductor device have limitations such that they must have heat and chemical resistances and must allow easy peeling of the support board from the semiconductor device.